a) Experimental setup: an SPP wave is launched by a hollow tip for near-field scanning optical microscopy in contact with the gold film. SPP propagation is imaged by collecting the light leaked into the substrate with a CCD camera placed in the focal plane of an oil immersion microscope objective (numerical aperture NA = 1.25). b) Example of an image collected by our experimental setup on the Au/Fe/MgO(001) sample. c–e) Scanning electron microscope images collected on Au/glass, Au/MgO(001), Au/Fe/MgO(001), respectively. Inset: LEED pattern collected on the Au/Fe/MgO(001) sample.